Devices of this type have already been proposed. Generally speaking, they comprise a waveguide and means for emitting infrared radiation.
The main difficulty of these devices is to ensure an efficient coupling between the waveguide and the emission means.
The article by J. Kasberger and B. Jakoby, “Grating-coupling of thermal radiation as an essential element of a fully integrated IR-absorption sensor system” may thus be cited, which appeared in OPTO Conference 2008 Proceedings, pages 161 and following.
This article describes a sensor whose operation is based on infrared absorption in the evanescent field region of a waveguide using thermally generated infrared radiation. The coupling between the thermal radiator emitting the infrared radiation and the waveguide is achieved by means of a network coupler.
However, the efficiency of the coupling obtained remains modest.
It should furthermore be noted that some solutions, known in the field of macroscopic optics, cannot be transposed to waveguides.
Thus, notably in photo-acoustics, thermal sources may be implemented in the form of filaments. However, they cannot be used with a waveguide owing to their high divergence.
For this reason, the solution which is widely adopted consists in coupling the waveguide to a laser source. Thus, laser sources have already been fabricated based on complex semiconductor structures.
They do however remain difficult to control and, to this today, their energy efficiency is fairly low, since it is of the order of 1/1,000.